Identification of Plasmodium berghei novel liver stage CD8 T cell epitopes by caged MHC class I tetramer technology (43.30)

Studies conducted in mice and humans have shown that IFN-γ+ CD8 T cell are the key effectors against liver-stage (LS) malaria; however, owing to complexities associated with the development of Plasmodia parasites, specificities of CD8 T cell effectors have been difficult to establish. Direct detection of Ag-specific CD8 T cells in high-throughput manner became possible with the development of caged MHC-tetramer technology, based on conditional photo-cleavable MHC class I ligands that can be displaced during UV induced exchange with a peptide of interest. On the basis of previously identified P. falciparum (Pf) genes expressed exclusively during LS infection, we identified P. berghei (Pb) orthologues of Pf genes and validated their expression by qRT-PCR in Pb infected C57Bl/6 mice. Several Pb LS antigens, administered as DNA vaccines, significantly reduced LS parasite burden in mice infected with Pb sporozoites. Using sequences of the 28 novel Pb LS genes we screened ~400 peptides by the caged MHC class I tetramer approach. Our preliminary results demonstrate that 2 H-2Kb- and 1 H-2Db-restricted Pb peptides that correspond to protective Pb LS Ags form MHC class I tetramers that specifically bound to CD8 T cells from mice immunized with radiation-attenuated Pb sporozoites. Identification of these epitopes is crucial towards resolving the role of antigen-specific CD8 T cell responses and establishing these responses as correlates of protection to Plasmodia infection.